Limitations with Other Radiotherapy Approaches:
Radiation Dose/Therapeutic Margin
A margin of normal tissue around the target lesion needs to be included to offset a variety of factors such as tumor motion, and degradation of full radiation dose around the tumor margins (due penumbra and radiation dose build up at any air-tumor interface). The addition of a larger therapeutic margin compensates for these deficiencies, but also increases the dose to adjacent normal tissue, making it difficult to deliver a large enough radiation dose to the tumor to exterminate it, without also risking serious injury to a critical adjacent structure such as normal lung, bronchus, heart, spinal cord or esophagus. Because of this normal tissue injury concern, the dose of radiotherapy is typically limited to 60-70 Gy in 6-7 weeks, while in reality; a far higher dose appears necessary to reliably sterilize even small bronchogenic carcinoma lesions (8). |
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